It is generally well-known to use organic dyestuffs, such as cyanine dyes and phthalocyanine pigments, in a recording layer of so-called writable recording media.
Recording systems of these recording media consist of applying a condensed laser beam on a very small area of a recording layer and converting the laser beam to a heat energy to change the properties of the recording layer (pit formation). For smooth change of the recording layer properties, generally spread media has a so-called air-sandwiched structure composed of a pair of substrates each having formed thereon a recording layer with the recording layers facing to each other. Recording of information on this type of recording media is carried out by irradiating a laser beam from the transparent substrate side to form optically readable pits in the recording layer. For reading, i.e., reproduction, of the recorded information, a laser beam having a weaker output than that for recording is irradiated on the recording layer to make a contrast between the pitted area and the non-pitted area, and the contrast is read out as electrical signals.
On the other hand, read-only-memory (ROM) type recording media having previously recorded information have been widely put to practical use in the field of audio recording and information processing. This type of recording media have no writable recording layer as used in the above-described writable recording media. That is, the ROM type recording media comprise a plastic substrate having previously formed thereon prepits by press forming, a reflective layer comprising a metal, e.g., Au, Ag, Cu, and Al, and a protective layer in this order. Such ROM type recording media are typically represented by compact discs (CD). The recording and reproduction signals on CD are standardized, and reproducing apparatus, called CD players, according to the standards are widely popular.
The above-mentioned writable recording media are similar to CD in use of a laser beam as a light source and in disc form. Hence, it has been keenly demanded to develop a writable recording medium which follows the standards of CD and can therefore be applied to a CD player. Several samples have been proposed to date to meet this demand. While the proposed samples conform to the standards as far as their initial characteristics are concerned, they turned out disadvantageous in that (1) they suffer from considerable jitter, (2) they are poor in duration of performance on repeated reproduction, (3) the recording layer has no light resistance, and (4) the recording sensitivity is uncontrollable.